‘核－壳’结构纳米材料入门

核壳结构纳米材料入门 1Nano-Chemistry,LZU,xxLecture9:g Semiconductingnanoparticles (3)core-shell nanostructuresNano-Chemistry,LZU,xxTodaySemiconductor-SemiconductorSemiconductor-MetalMetal-Polymer Metal-MetalMetal-SemiconductorNano-Chemistry,LZU,xx1.21Energy Banddiagram ofdifferent materialsFreeelectronsE FE0Vacuum levelFermilevel(Valence band)(conduction band)(band gap)E0E FMetalSemiconductorNano-Chemistry,LZU,xxSemiconductor Quantum WellNano-Chemistry,LZU,xxWhat are2D,1D,0D nanosturectures?Nano-crystallite ofsemiconductor materialthat confinescarriers(electrons andholes)in all three dimensionsQuantumWell2DQuantum Wire1DQuantum Dot0DBohr nexciton radiusis thecriticaldimensionDensity ofstates(DOS)Nano-Chemistry,LZU,xxMolecule,e Nanoparticleand aBulk SemiconductorMOLECULELUMOHOMOCBVBEgBULK SOLID?E?EEnergyNANOPARTICLE2Nano-Chemistry,LZU,xxInorganic SemiconductorsTrapstates arecaused bydefects,such asvacancies,local latticemismatches,dangling bonds,or adsorbatesat thesurfaceNano-Chemistry,LZU,xx2.2Semiconductor NanoparticlesQuantumdots aresemiconductors particlesthat hasallthreedimensions confinedto the1-100nm lengthscaleGroup14(old groupIV)Si,GeIII-V Materials:GaN,GaP,GaAs,InP,InAsII-VI Materials:ZnO,ZnS,ZnSe,CdS,CdSe,CdTeColloidal CdSequantum dotsdispersed inhexaneNano-Chemistry,LZU,xx3.Core-shell nanoparticlesNanoparticle Engineeringand SurfaceModification coreshellNano-Chemistry,LZU,xxWhy Core-Shell?Tuning ofPhysical PropertiesChemicaland ColloidalStability?Nanoparticle degradationthrough chemicaletching?Agglomeration causedby strongvan derWaals attractiveforces?Collective properties of nanoparticleassemblies are influenced to a largeextent bythe separationbetween theparticles.?Coating theparticles witha uniformshell ofinert materialcould controlthe distancebetween theparticlesControl ofe InterparticleInteractions WithinAssembliesFor example,the opticalpropertiesofmetal nanoparticlesareinfluencedby theirenvironments.Controlled surfacemodification canalter thesepropertiesNano-Chemistry,LZU,xxTypes of Core-Shell Nanoparticles?Semiconductor-Semiconductor?Semiconductor-Metal?Metal-Polymer?Metal-Metal?Metal-SemiconductorNano-Chemistry,LZU,xx3.1Semiconductor-Semiconductor core-shell structures3Nano-Chemistry,LZU,xxEnergies ofVarious Semiconductors1.4GaAs2.25GaP1.7CdSe2.5CdS3.2ZnO3.2WO33.2TiO23.0TiO2Energy(eV)Values atpH=1Nano-Chemistry,LZU,xxSemiconductor onSemiconductorTailoring opticalpropertiesEnhancing theluminescence of the coreCoreShellcoreshell coreshellEnergyNano-Chemistry,LZU,xxExamples forSemiconductor-Semiconductor Core-Shell NanoparticlesJ.Phys.Chem.B.1997,101,9463J.Phys.Chem.B.1998,102,1884J.Phys.Chem.1993,97,5333J.Phys.Chem.1996,100,6381J.Phys.Chem.1996,100,8927J.Phys.Chem.1996,100,13226J.Phys.Chem.1996,100,xx1Examples include:ZnS onCdSeCdS onCdSeCdSe onCdS,etcNano-Chemistry,LZU,xx3.1.1CdSe Coatedwith ZnSNanoparticlesMe2Cd+TOPSe CdSe?T300o C(TMS)2/Me2Zn/TOPCdSeZnSTEM pictureof(CdSe)ZnS nanocrystalsJ.Phys.Chem.1996,100,468Nano-Chemistry,LZU,xxCdSe Coatedwith ZnSNanoparticlesJ.Phys.Chem.1996,100,468Absorption spectrumof the(CdSe)TOPO(dotted line)and the(CdSe)ZnSnanocrystals(solid line).The fluorescenceof the(CdSe)ZnS isalso shown(solid line)Normalized fluorescencespectra of CdSe-TOPO(dotted line)and CdSeZnS(solid line)with470nm excitationNano-Chemistry,LZU,xxObservations onthe OpticalCharacteristics of CdSe/ZnS NanoparticlesFluorescenceof CdSe-TOPO showsthe broadtail,due tosurface traps.CdSe/ZnS fluorescencespectrum hasa flatbaseline;this indicatesthat theZnS reducesthe trapspresent onthe CdSe(TOPO)surfaceFluorescence ofCdSe(CdSe/ZnS)was stablefor monthspared touncapped CdSeNoreduction in the CdSequantum yieldwas observedfor monthswith theCdSe/ZnS nanoparticlesJ.Phys.Chem.1996,100,4684Nano-Chemistry,LZU,xx(Top)Emission spectra of severalsizes ofCdSe-ZnS quantumdots,with excitationat350nm inall cases.(Bottom)Idealized mixed-surface QD-protein conjugate.Antibodies labeledwith biotin(生物素)bind efficientlyto QDsurfaces dueto thegreat strengthof theirinteraction withbridging avidin(抗生物素蛋白抗生物素蛋白)molecules Nano-Chemistry,LZU,xx3.1.2Synthesis of HgS/CdS Core-Shell NanostructuresHgS core CdSshellHgCl2+H2S+sodium polyphosphateHgSHgS+Cd(ClO4)2+H2SHgS/CdSCdS coreHgS shellCd(ClO4)2+H2S+sodium polyphosphateCdSCdS+HgCl2+H2SCdS/HgSJ.Phys.Chem.1993,97,5333Note:Due tothe muchlower solubilityofHgSpared withCdSparticles resultin anexchange ofCd2+by Hg2+(CdS)n+mHgCl2(CdS)n-m(HgS)m+mCdCl2Nano-Chemistry,LZU,xxCdS/HgS MixedColloidsHgS nanoparticlesHgScoated withCdSJ.Phys.Chem.1993,97,5333Nano-Chemistry,LZU,xxAbsorption Spectraof Core-Shell CdSonHgS NanoparticlesA=HgSJ.Phys.Chem.1993,97,5333More CdSNano-Chemistry,LZU,xxFluorescence SpectraofCore-Shell CdSonHgS NanoparticlesHgSnanoparticles donot fluoresceCdScoated HgSnanoparticles fluoresce:Possibly dueto removalof trapsfor nonradiativerebinationsorFluorescencecould arisefrom bandto bandrebination inHgScoreJ.Phys.Chem.1993,97,5333More CdSNano-Chemistry,LZU,xxCdS/HgS MixedColloidsJ.Phys.Chem.1993,97,53335Nano-Chemistry,LZU,xx3.2Metal coreNano-Chemistry,LZU,xx3.2.1Oxide onMetals?Main reasonis fornanoparticle stabilization?Could alsobe usedto assemblenanoparticles?Examples:Chem.Mater.1998,10,1214J.Am.Chem.Soc.1999,121,8518Adv.Mater.1999,11,34Adv.Mater.1998,10,132Chem.Commun.1998,351Adv.Mater.1999,11,131J.Am.Chem.Soc.1999,121,10642Nano Lett.xx,2,3Nano-Chemistry,LZU,xxFormation of a thin silica shellon citrate-stabilized goldparticles(SiO2Au)Langmuir1996,12,4329Nano-Chemistry,LZU,xx15nm SiO2AuThe silica shell keepson growing,but eventuallysmall silicaparticles alsonucleate outof thesolution.18hours afteraddition ofactive silica42h afteraddition5days afteradditionLangmuir1996,12,4329Nano-Chemistry,LZU,xxSiO2Au NanoparticlesTransmissionelectron micrographsof silica-coated goldparticles producedduring theextensive growthof thesilicashellaround15nm Auparticles withTES in4:1ethanol/water mixtures.The shellthickness are(a,top left)10nm,(b,top right)23nm,(c,bottom left)58nm,and(d,bottom right)83nmLangmuir1996,12,4329Nano-Chemistry,LZU,xxInfluence ofthinsilicashells onthe UV-visible spectra of aqueousgold colloidsExperimentalCalculatedLangmuir1996,12,43296Nano-Chemistry,LZU,xxEffect ofSolvent RefractiveIndex Thesolvent refractiveindices(left toright)are1.45,1.42,1.39,and1.36Langmuir1996,12,4329Nano-Chemistry,LZU,xxSilica Coatingof SilverColloidsLangmuir1998,14,3740AgClO4+sodium citrate10nm Ag nanoparticles NaBH4Agnanoparticles+3-aminopropyltrimethoxysilane+sodium silicateAgSiO2Silicate ionconcentration0.02%0.01%0.005%Nano-Chemistry,LZU,xx3.2.2Polymer-Coated Silver NanoparticlesJ.Am.Chem.Soc.1999,121,10642TEM imagesof silverparticles:(A)uncoated particle,(B)polystyrene/methacrylatecoated particles,(C)polystyrene/methacrylate coatedparticles witha covalentlybound BSAlayer,and(D)the sameas panelC afterexposure togold colloids.Negative stainingby phosphotungsticacid usedfor allimagesNano-Chemistry,LZU,xxPreparation ofPolymer-Coated FunctionalizedSilverNanoparticlesExtinction spectraof silverparticles:(A)uncoated particlesand(B)polystyrene coatedparticles.Solid line:suspension inwater.Dotted line:suspension inwater,after1h in1.8M NaClJ.Am.Chem.Soc.1999,121,10642Nano-Chemistry,LZU,xxAssembly ofNanoparticle arraysProceduresfor(A)Ppy-linked Au ColloidsAlkyldithiolate-Linked AuColloidsChem.Mater.1998,10,1214Ppy=poly(pyrrole)Nano-Chemistry,LZU,xxAuColloidsLinked byPPyTransmission electronmicroscope imagesof1D andnear-1D arraysof Aucolloids linkedby PpyChem.Mater.1998,10,12147Nano-Chemistry,LZU,xx3.2.3MetalMetal Core-Shell NanostructuresExamples reportedin theliteratureAu/Ag:J.Chem.Phys.1964,41,3357-3363Au/Cd:Ber.Bunsenges.Phys.Chem.1994,98,180-189Au/Pb:Ber.Bunsenges.Phys.Chem.1994,98,180-189Au/Sn:J.Phys.Chem.1994,98,6931-6935Au/Tl:Ber.Bunsenges.Phys.Chem.1994,98,180-189Ag/Pb:Ber.Bunsenges.Phys.Chem.1992,96,754-759Ag/Cd:J.Phys.Chem.1994,98,6931-6935Ag/In:Ber.Bunsenges.Phys.Chem.1992,96,2411-2414Au/Pt:J.Phys.Chem.B.2000,104,2201-2203Nano-Chemistry,LZU,xxPt/Au Core-Shell NanoparticlesPtCl42-+sodium polyacrylatePt nanoparticles(12nm)Pt nanoparticles+K2Au()2Pt/AuH2-raysMeOHSynthesis of Pt coreAu shellNanoparticlesSynthesis of Au corePt shellNanoparticlesJ.Phys.Chem.B.2000,104,2201-2203NaAuCl4+sodium citrateAu nanoparticles(20nm)PtCl42-+Au nanoparticles Au/PtH2High TNano-Chemistry,LZU,xxPt coreAu shellNanoparticlesPt nanoparticles1:1Pt/Au nanoparticles1:2Pt/Au nanoparticlesJ.Phys.Chem.B.2000,104,2201-2203Nano-Chemistry,LZU,xxPt/Au Core-Shell NanoparticlesAbsorptionspectraofPt nanoparticlesbefore and after deposition of variousamounts ofgold.Overall Ptconcentration is1x10-4M ConcentrationofPt:Au isgiven onthe curvesAbsorptionspectraof Au nanoparticlesbefore andafter depositionof variousamounts ofPt.Overall Auconcentration:3x10-4M Molarof Au:Pt isgiven onthe curvesJ.Phys.Chem.B.2000,104,2201-2203Nano-Chemistry,LZU,xxAu corePt shellNanoparticlesElectron micrographof Au core particlesbefore(left)andafter(right)depositionofPt inthe ratio1:2J.Phys.Chem.B.2000,104,2201-2203Nano-Chemistry,LZU,xx3.3Metal-Semiconductor Core-Shell NanoparticlesMetalscan beused astemplates tomake hollowsemiconductor nanostructuresFabricationof positenanoparticles witha largeelectronic capacitance,i.e.a largedifference inthe Fermilevel of the corerelative tothe conductionband edgeof theshell willenable electronsto diffusethrough theshell andbe trappedinthecore fora longtimeExamples:Au/CdSe:J.Mater.Res.1998,13,905-908Au/CdS:J.Phys.Chem.B.1997,101,7675Ag/TiO2:Langmuir2000,16,2731-2735Au/TiO2:J.Phys.Chem.B.2000,104,10851TiO2/Ag:Langmuir1999,15,7084-7087ZnO/Au:J.Phys.Chem.B.xx,107,7479-74858Nano-Chemistry,LZU,xx3.3.1CdS/Au CompositeNanoparticlesAu nanoparticlesCdS/Au positenanoparticlesJ.Phys.Chem.B.1997,101,7675Nano-Chemistry,LZU,xxSynthesis ofCdS-Capped AuNanoparticlesNaAuCl4+sodium citrateAu nanoparticles(20nm)High TMNA=2-mercaptonicotinic acidJ.Phys.Chem.B.1997,101,7675Nano-Chemistry,LZU,xxAbsorption Spectraof Au/CdSNanopositesAuAu/MNACdSAu/CdSAbsorption propertiesofAu/CdS arenot theresult ofa simpleaddition of the spectraof twonanoclusters,but ratheran influenceof theCdS onthe Au.J.Phys.Chem.B.1997,101,7675Nano-Chemistry,LZU,xxEmission SpectraofCdS/AuNanopositesJ.Phys.Chem.B.1997,101,7675Emission quenchingofCdSis indicativeoftheourrence ofelectron transferfrom excitedCdSinto theAucore.Conduction bandenergy forCdS=-1.0V vs.NHEFermi levelofAu=+0.5V vs.NHENano-Chemistry,LZU,xx结语*核壳结构和组成千变万化，相应的材料化学内容极为丰富；*很多核壳复合材料具有意想不到的功能，应用前景十分广阔；*核壳复合材料的结构与性质或功能的关系还不是很清楚，相应的理论工作大有可为。 *核壳结构和组成千变万化，相应的材料化学内容极为丰富；*很多核壳复合材料具有意想不到的功能，应用前景十分广阔；*核壳复合材料的结构与性质或功能的关系还不是很清楚，相应的理论工作大有可为。 Nano-Chemistry,LZU,xxHomeworkWhen excitedby light,what wouldhappen tothe twonanoparticlesAand B?CoreShellcoreshell coreshellEnergyBA9Nano-Chemistry,LZU,xxArt ofcore-shell nanostructures？Triangular andFibonai NumberPatterns Drivenby Stresson Core/Shell MicrostructuresChaorongLi,Xiaona Zhang,Zexian Cao*Institute ofPhysics,Chinese Academyof Sciences,SCIENCExx,309,909Nano-Chemistry,LZU,xxFibonai numberpatterns onAg core/SiOx shellstructureSCIENCExx,309,909Nano-Chemistry,LZU,xxFibonai Number?斐波纳契数The sequence begins withone.Each subsequentnumber isthe sumofthetwo precedingnumbers.Fib(n)=Fib(n-1)+Fib(n-2)Thus thesequencebeginsas follows:1,1,2,3,5,8,13,21,34,55,89,144.Nano-Chemistry,LZU,xxThe storyof Fibonaiand rabbits.Long glong ago.Fibonai appliedhis sequencetoaproblem involvingthe breedingof rabbits.Given certainstarting conditions,he mappedout thefamily treeofagroup of rabbits thatinitially startedwith onlytwo